Different types of acoustic devices have been used through the years. One type of device is a microphone. In a microelectromechanical system (MEMS) microphone, a MEMS die includes a diagram and a back plate. The MEMS die is supported by a substrate and enclosed by a housing (e.g., a cup or cover with walls). A port may extend through the substrate (for a bottom port device) or through the top of the housing (for a top port device). In any case, sound energy traverses through the port, moves the diaphragm and creates a changing potential of the back plate, which creates an electrical signal. Microphones are deployed in various types of devices such as personal computers and cellular phones.
Various types of problems can arise as microphones are operated. Total harmonic distortion (THD) can be thought of as the level of distortion or nonlinearity of output signals. Output signal can be considered linear if the input signal can be represented by using the output signal by multiplying the output signal with a constant value. More specifically, THD can be defined as the ratio of the sum of the powers of all harmonic components of a signal to the power of the fundamental frequency of the output signal. The less the THD, the better the signal quality of the microphone.
Previous approaches have not always proven satisfactory for reducing THD and this has resulted in some user dissatisfaction with these previous approaches.